I suppose the key word here is "Approved". Most manufacturers have had schedules in their manuals but they were not "approved" by the CAA.
So the CAA published LAMS/LAMPS which although very generic is approved.
As I previously mentioned there is no problem getting a manufacturers schedule approved, but in my experience in GA most owners will not want to go to this expense.
BTW I have checked with a friend of mine who had a scheduled approved by the CAA & it was FREE!.